1. Field of the Invention
The present invention relates to a directional coupler which, for example, extracts portions of output signals, and outputs the extracted portions of signals as feedback control signals, and particularly relates to a directional coupler used for an output monitor of mobile communication equipment such as a cellular telephone, and other such devices.
2. Description of the Related Art
Conventionally, directional couplers take advantage of a phenomena wherein, in the event that two conductor patterns with xc2xc wavelength of the usage frequency are arranged so as to be mutually parallel with one of the conductor patterns as a main line, applying signals to the main line results in signals that are proportionate to the voltage propagating the main line being output at one end of the other line. Such directional couplers are in widespread use as output adjusting monitors for cellular telephones, and other suitable devices.
FIG. 27 is a model plan view illustrating an example of a directional coupler. This directional coupler 100 includes an insulating member 200, and a main line 300 and sub line 400 formed on the insulating member 200. The main line 300 and sub line 400 are partially parallel with a gap therebetween, and it is at this parallel portion that coupling occurs. The sub line 400 can extract a portion of the signals flowing along the main line 300 by the coupling.
For example, in the event that such a directional coupling is assembled into a cellular telephone, the directional coupler 100 is used at the high-frequency amplifier circuit of the transmitting side. One end 300xcex1 of the main line 300 is connected to the high-frequency amplifier circuit, while the other end 300xcex2 is connected to an antenna. Also, one end 400xcex1 of the sub line 400 is connected to a circuit that controls the high-frequency amplifier circuit, and the other end 400xcex2 is terminated at a terminating resistor. The sub line 400 extracts (detects) a portion of the voltage passing through the main line 300, and the detected signals are sent to the circuit for controlling the high-frequency amplifier circuit, where high-frequency voltage output from the high-frequency amplifier circuit is controlled by this circuit, thereby maintaining the intensity of signals emitted from the antenna within a predetermined range.
Incidentally, loss which occurs upon being input from the one end 300xcex1 of the main line 300 and output at the other end 300xcex2 is referred to as xe2x80x9cinsertion lossxe2x80x9d, and voltage input from the one end 300xcex1 of the main line 300 and output at the other end 400xcex1 of the sub line 400 is referred to as xe2x80x9cdegree of couplingxe2x80x9d. Also, the minute voltage observed at the other end 400xcex1 of the sub line 400, as opposed to the voltage output at the input end 300xcex1 which is voltage input from the one end 300xcex1 of the main line 300 but reflected within the coupler or at the output end (other end) 300xcex2 and output at the input end 300xcex1, is referred to as xe2x80x9cisolationxe2x80x9d. Further, the ratio of the xe2x80x9cdegree of couplingxe2x80x9d and xe2x80x9cisolationxe2x80x9d is referred to as xe2x80x9cdirectivityxe2x80x9d.
Now, directional couplers 100 are being reduced in size, due to the devices in which they are being assembled, such as cellular telephones, being reduced in size. This reduction in size requires reduction in the length of the parallel portion between the main line 300 and the sub line 400. This causes a problem in that a sufficient degree of coupling cannot be obtained.
Accordingly, an arrangement can be conceived to reduce the gap between the main line 300 and sub line 400, in order to obtain sufficient coupling. However, excessively narrowing the gap may result in insulation destruction between the main line 300 and sub line 400, so there is a limit to how narrow the gap between the main line 300 and sub line 400 can be, and satisfactory coupling cannot be obtained by this arrangement. Accordingly, a directional coupler 100 such as shown in FIG. 28 has been proposed. With this directional coupler 100, sub lines 400A and 400B are arranged in parallel on both sides of the main line 300 with gaps therebetween, and both ends of the sub lines 400A and 400B are each short-circuited. This configuration attempts to obtain satisfactory degree of coupling by increasing the sub line portion that is parallel to the main line 300.
Also, as another proposal, an arrangement can be conceived wherein the width of the lines 300 and 400 are narrower, thereby disposing long lines on the insulating member 200. However, in this case, an increase of loss of line increases the insertion loss, resulting in increased electric power consumption of the equipment in which the directional coupler 100 is assembled. This leads to the problem of reduced driving time with cellular telephone terminals and other devices which are generally driven by batteries.
Also, an arrangement can be conceived wherein the lines are longer in order to raise the degree of coupling, but making the lines longer causes the problem of increased insertion loss occurring.
On the other hand, as a result of a reduced permissive area for forming the conductor patterns due to reduction in size, there are problems in that securing sufficient line length is difficult, and in that consistency with circuits to which connection is made becomes poor, leading to deterioration in reflection properties. That is, the size of directional couplers is being reduced by forming the lines to have meandering, spiral, or helical configurations, thereby reducing the area and volume necessary for forming the conductor patterns.
Particularly, in the event of forming the lines (conductors) to have spiral or helical shapes, the inductance component can be efficiently obtained, and thus is advantageous in that the length of the lines to be formed can be reduced.
However, in the event that the lines (conductors) are formed to have spiral or helical shapes, there is the problem that deterioration in isolation properties occurs. Isolation properties can be improved by adjusting the gap between the main line and the sub line, and so forth, but in this case, the coupling between the main line and the sub line is low, so in practice, it is difficult to improve the directivity, which is the ratio between the degree of coupling and the isolation.
In order to solve the above-described problems, preferred embodiments of the present invention provides a small and high-capability directional coupler which has excellent isolation properties and directivity while maintaining a desired degree of coupling, with minimal deterioration in insertion loss and reflection properties.
According to a preferred embodiment of the present invention, in a directional coupling device, line coupling (distributed constant coupling) is effected between a main line and a sub line by positioning at least a partial region of a main line and sub line substantially parallel with one another when viewed in a planar manner, and the line length of the sub line is longer than the line length of the main line.
With a side edge type directional coupler wherein line coupling (distributed constant coupling) is effected between the main line and the sub line by positioning at least a partial region of a main line and a sub line substantially parallel with one another, forming the line length of the sub line to be longer than the line length of the main line improves isolation properties, and the desired degree of coupling can be obtained while securing directivity.
Also, there is no lengthening of the main line, so the insertion loss is not increased and deterioration in reflection properties is prevented, and the electric power consumption in battery-driven mobile communication equipment is minimized.
Note that the phrase xe2x80x9cline coupling (distributed constant coupling) is effected between the main line and sub linexe2x80x9d in preferred embodiments of the present invention is a concept indicating that the main line and sub line are coupled by distributed constant coupling from the capacity component C and inductance component L, and does not encompass coil coupling such as two coils being electromagnetically coupled.
Also, the directional coupling device may have the main line formed as a substantially straight line or a substantially straight line which bends at a predetermined position but not a line which circles in spiral fashion, the sub line being a line which circles in spiral fashion by bending a substantially straight line at a plurality of predetermined positions.
Forming the sub line so as to have a spiral shape to extend the length thereof enables a high degree of coupling to be obtained, while keeping isolation low.
Also, the length of the main line can be made shorter than the sub line, so an increase in insertion loss of the main line can be prevented in a reliable manner, and decay of signals can be prevented in battery-driven terminals, so signals can be efficiently transmitted. Consequently, this enables long driving times for battery-driven terminals.
Also, forming the main line as a substantially straight line or a substantially straight line bending at a predetermined position, i.e., a non-spiral line, and forming the sub line to have a spiral configuration by bending a substantially straight line at a plurality of predetermined positions, enables a highly-reliable directional coupler with desired properties to be provided, without requiring complicated line patterns.
Also, the main line and sub line may be embedded in an insulating member of a layered structure including a plurality of insulating layers that have been stacked on each other.
Embedding the main line and sub line in an insulating member having a layered structure including a plurality of insulating layers that have been stacked raises the line density, thereby enabling further reduction in size of the directional coupler.
Also, line coupling of the sub line to the main line may be effected by a portion of the sub line being disposed on both sides of the main line at a predetermined region of the main line.
With a configuration wherein the sub line is disposed on both sides of the main line at a predetermined region of the main line, an even higher degree of coupling can be obtained due to the coupling between the main line and the sub lines on either side thereof.
Also, line coupling of the sub line to the main line may be effected by a portion of the sub line being disposed above and below the main line with the insulating layer being disposed therebetween.
With an arrangement wherein the main line and sub line layered with the insulating layer disposed therebetween are made to face one another (i.e., to be superimposed with the insulating layer introduced therebetween), thereby effecting line coupling (distributed constant coupling) between the main line and sub line, directional couplers with various degrees of coupling can be readily obtained by simply adjusting the thickness of the insulating layer, even without changing the line pattern, and small high-capability directional couplers can be obtained. Also, with this arrangement as well, forming the line length of the sub line to be greater than the line length of the main line improves isolation properties, and the desired degree of coupling can be obtained while securing directivity, and moreover, there is no lengthening of the main line, so occurrence of increases in insertion loss and deterioration in reflection properties can be prevented, and the electric power consumption in battery-driven mobile communication equipment is minimized.
Also, line coupling of the sub line to the main line may be effected by a portion of the sub line being disposed at two of the following locations: at least one side of the two sides of the main line; above the main line; and below the main line.
As a result of such a novel arrangement and configuration, the length of the electromagnetically coupled portion between the sub line and the main line can be significantly extended, without increasing the size of the substrate. Accordingly, the degree of coupling between the main line and sub line is increased, and directivity is improved even more.
Also, the main line and the sub line may be formed by photolithography using at least one of photosensitive electroconductive material and photosensitive resist, or other suitable material.
Forming the main line and the sub line by photolithography using at least one of photosensitive electroconductive material and photosensitive resist, or other suitable material, enables fine and highly-precise line patterns to be formed, thereby yielding a directional coupler having the desired properties.
Also, the line width of the main line may be greater than the line width of the sub line.
In the event that the line width of the main line is greater than the line width of the sub line, loss at the time of signals passing through the main line is minimized, so efficient signal transmission with suppressed electric power consumption can be realized.
Other features, elements, advantages and characteristics of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.